Generally speaking, air-conditioners consist of one or more outdoor units and one or more indoor units connected via refrigerant piping defining a refrigerant circuit. The outdoor and indoor units each comprise a heat exchanger for, on the one hand, exchanging heat with the heat source and, on the other hand, exchanging heat with the space to be conditioned. Outdoor units of air-conditioners are in most cases installed outside a building for example on the roof or at the facade. This, however, has under certain circumstances been perceived as disadvantageous from an aesthetical point of view. Therefore, EP 2 108 897 A1 suggested to integrate the outdoor unit into a ceiling of the building so as to be hidden therein and not to be noticeable from the outside of the building.